In the food industry, it is frequently necessary to dose, pump, mix and blend liquids. Continuous mixing processes can be implemented directly in piping using ratio-based or Blendline control systems, which remove the need for mixing containers. In smaller batch processes, the required components are dosed and mixed in containers one after the other using suitable flowmeters and counting equipment.
Components can also be dosed at a later stage after technical and sensory analyses. Not all systems are large enough to justify the investment in a control system, it may be more economical to use individual counters. The following description outlines a number of potential applications and implementation methods for batch dosing using individual counters.
Implementation using an electromagnetic flowmeter with an internal counter
The electromagnetic flowmeter FEH500 with an internal counter can be used directly for batch dosing. Dosing times must be longer than three seconds for this purpose. An internal pre-settable counter, which can also be adjusted directly on the device, is installed in the flowmeter transmitter. Batches can be started via an external contact and stopped via the counter’s output contact.
If a pre-contact is available, this can also be used in connection with a suitable valve to slow dosing at the end of the batch before the main contact terminates the entire process. To improve accuracy for short dosing processes, the device is equipped with automatic overrun correction, whereby the transmitter measures the quantity that continues to flow after its close command, thus indicating excess dosing.
Calculations are performed to determine the length of time by which the transmitter’s close command should be moved forward in subsequent cycles in order to ensure accurate dosing.
This is a cost-effective solution which is simple to implement as no additional counter is required. One drawback of this arrangement is that inputs must always be made directly at the device in the piping (if the flowmeter has an integral mount design), and in-process counter readings are therefore laborious.
Centralisation may also pose a challenge if several components are used. The dosing process is enabled via a contact input on the flowmeter which resets the internal counter. Any additional control functions required must be implemented via hardware or a PLC.
Implementation using a Coriolis mass flowmeter and indicator/totaliser
Use of an ABB type CM15 indicator as a counting device makes reading and operating procedures more convenient. The indicator can be installed in a measuring station or another easily accessible location.
The intuitive operating buttons positioned directly on the indicator can be used for pre-selection purposes. An additional button or a contact on the indicator’s binary input can be used to start the batch. If extra operating options and control functions are required, these must be implemented via additional buttons/switches and hardware, and the contacts can of course also be controlled via a PLC.
Implementation using a flowmeter and compact controller AC500eco
An ABB AC500eco compact controller can be used as a counter and control device if the options provided by the above solution fall short of what is required. One or more pre-setting counters can be programmed in a controller of this kind, and control parameters such as locks, interruptions and similar can be implemented.
A touchscreen is used to operate the device as well as to display pre-set quantities, the flow counter, and buttons and switches. The counter can only display figures up to 64 000, but this does not generally present a problem since the counter is only used as a dosing counter for limited quantities rather than as a flow counter.
Implementation of a filling application using a rapid mass flowmeter, AC500eco and rapid Modbus connection
Very short dosing processes such as those frequently required by filling applications can be achieved by combining a Coriolis mass flowmeter and the AC500eco with a rapid Modbus connection used for communications between the two. The controller features software which has been specially developed for filling processes. The system also records any overrun quantities after the close command and can perform self- corrections. Filling times must be greater than or equal to three seconds.
For more information contact ABB South Africa, +27 (0)10 202 6459, [email protected], www.abb.com/za
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